Three genes of miraculin-like proteins from Nicotiana benthamiana with dissimilar putative structures show highly similar patterns of induction following bacterial and fungal infections

Abstract

Expression of three Nicotiana benthamiana miraculin-like protein genes, NbMLP1, NbMLP2 and NbMLP3, showed almost identical responses to wounding, an incompatible interaction with Pseudomonas syringae pv. tabaci and compatible interactions with P. syringae pv. tabaci, Colletotrichum destructivum or Colletotrichum orbiculare. However, only NbMLP1 expression responded to exogenous methyl jasmonate or ethylene. None exhibited expression in healthy leaves and stems, and all showed highest expression in seeds, except for NbMLP1, which had highest expression in roots. NbMLP1, NbMLP2 and NbMLP3 were in different subfamilies of miraculin-like protein sequences of N. benthamiana and Nicotiana tabacum. Subfamilies correlated well with predicted features of the reactive-site loop potentially affecting the bond that could react with serine proteinases. Despite considerable predicted structural diversity that might affect biological activity, the apparently coordinated expression of these genes to pathogen attack may reflect the need to produce diverse proteinase inhibitors to act against a potentially broad range of secreted microbial proteinases during basal resistance to pathogens.